The present invention relates to a device to effect a fluid-tight coupling around a pipe serving to convey molten material, as part of the connection between a low pressure diecasting machine and a pressurizable receptacle in which the molten material is prepared. The device disclosed is well suited for application to a pipe fashioned from fragile material, insertable typically through one wall of the receptacle, which comprises a body having an inlet end that is located internally of the receptacle and a head at the pipe outlet end whose surface can be coupled in fluid-tight association with a mold coupled to the low pressure diecasting machine.
A low pressure diecasting machine of the type in question is mounted on and connected to a receptacle containing molten material in a manner such that the pipe is aligned and connected with the injection nozzles of a mold connected to the machine.
The prior art systems employed in making such a connection, while based on a variety of techniques, are similar inasmuch as all permit removing the machine from the receptacle. In effect, the machine rests on the receptacle during operation and can be moved to a non-operating position whenever the need arises to gain access to the inside of the receptacle. To ensure the features of a removable connection that can be successfully operated, the pressure-tight fit between the nozzles and the front end surface of the head of the pipe is obtained by interposing seals of gaskets of suitable thickness. The efficiency of the sealing action in containing the pressure of the molten material is somewhat critical, given that the tightness of the fit between the front end surface of the pipe and the nozzle of the mold relies only on a suitably strong force of compression.
In practice, this is achieved by packing the space between the machine and the head of the pipe to an overall depth nominally greater than that of the existing gap, so that the fluid-tight barrier will be established by a compressive force provided by the total weight of the low pressure diecasting machine.
Quite apart from the operational inconvenience and the empirical nature of such a system, selection of the optimum condition depends on a process of trial and error. The working principle underlying this method of connection tends to result in a high degree of structural stress on the pipe. In other solutions, the receptacle is forced vertically into association with the diecasting machine through the agency of suitable lifting means, the force in this instance being applied laterally.
Owing to the intense and uncontrollable impact of these stresses, rupture of the pipe frequently occurs, particularly when the pipe, as already intimated, is made of a fragile material, such as silicon nitride or other ceramics typically utilized in the context of low pressure diecasting processes for aluminum alloys.
Conversely, the application of a smaller compressive force to the sealing medium might well diminish the risk of pipe rupture, but would not ensure an efficient sealing action to accommodate the pressure of the fluid flowing at high temperature through the pipe. In short, a solution that succeeds both in avoiding the risk of rupture to the pipe and in ensuring an efficient seal must necessarily involve a compromise between the two opposing requirements outlined above.